Which one of the following has been constituted under the Environment (Protection) Act, 1986?

The correct option is Central Ground Water Authority.

Here is the step-by-step educational explanation of why this option is correct:
1. Constitutional Basis: The Central Ground Water Authority (CGWA) was constituted under Section 3, Subsection (3) of the Environment (Protection) Act, 1986. This authority was created following the directives of the Supreme Court of India to address the urgent need to regulate groundwater extraction.
2. Mandate and Functions: The primary mandate of the CGWA is to regulate, control, and manage groundwater development and resources in the country. It has the power to issue guidelines, declare resource-stressed areas as 'notified' zones, and grant No Objection Certificates (NOCs) for groundwater extraction to industries, infrastructure projects, and mining sectors.
3. Analysis of the Other Options:
- Central Water Commission (CWC): This is a premier technical organization in India in the field of water resources, established much earlier in 1945.
- Central Ground Water Board (CGWB): Established in 1970 under the Ministry of Agriculture (later merged with the Ministry of Water Resources), it is a multidisciplinary scientific organization responsible for national policies on ground water assessment, monitoring, and exploration, rather than a regulatory authority constituted under the 1986 Act.
- National Water Development Agency (NWDA): Established in 1982, it is an autonomous society registered under the Societies Registration Act, 1860, carrying out feasibility studies for the interlinking of river systems.